This invention relates to a polymer transfer and deposition system and to a carrier transfer molding system where a carrier of a generally planar shape passes below a polymer deposition device where polymer is deposited on the carrier with the combined carrier and polymer moving to a forming device to produce an article of a desired shape. When more than one layer of polymer is deposited on the carrier, an insert is placed between the polymer layers. A surface layer is laminated to the top layer of polymer prior to moving into a forming device.
This invention refers to a transport and deposition device and method as described in U.S. patent application Ser. No. 09/388,052 filed on Sep. 1, 1999, now U.S. Pat. No. 6,264,462. issued Jul. 24, 2001.
This invention relates to a system including a combined carrier and deposited polymer that move into a forming device to produce an article of a desired shape. The carrier may collect more than one deposit or layer of polymer where an insert such as a rigid foam or honeycomb core is encapsulated by the polymer layers. Additionally, continuous strands of fiber reinforcement may be incorporated in the polymer phase. The carrier, as an example, is a film, foil, fiber construction or other support of a generally planar shape. The carrier provides a decorative surface in the finished shape, outdoor ultra-violet (UV) protection, fire retardency, improved chemical and permeation resistance, improved impact properties or just provides a sacrificial mechanism to move a deposited polymer into a forming device. Although a thermoset can be specified as the deposited polymer, a molten thermoplastic is the preferred choice. A method to deposit polymer onto a carrier in close proximity to one or more forming devices, to minimize heat loss time prior to forming the desired part, is described in my copending U.S. patent application, Ser. No. 09/388,052, now U.S. Pat. No. 6,264,462. The same disclosure describes a method to incorporate continuous fibers in the polymer composition.
Although the carrier process or method can produce a wide variety of sizes and shapes, the processing advantages become more apparent as the size of the finished part increases, typically in excess of one square meter. A prime thermosetting method used to produce large polymer composites utilizes cross-linking liquid resins to impregnate reinforcements under low pressures, either within a mixing head or pumping the liquid into a fiber preform. The combined composite solidifies as the liquid polymer cross-links. Large thermoplastic composites can be produced under low pressure by a softening a plastic sheet, then pulling a vacuum under a forming shape. These low pressure processes are generally used where production volumes are lower because of the lower productivity associated with these technologies. Injection molding was designed for high volume production of polymer shapes. However, the process requires higher molding pressures. For large parts, these pressure requirements can be substantial. The increasing equipment costs associated with the need to meet increased pressures has limited the use of injection molding in the production of large parts.
The polymer deposited on a carrier generally occupies or fills out a large area of the forming dies in a forming press, plus the pre-coating of the carrier by a deposited polymer, leads to a reduction in trapped gases between the carrier and the polymer. Because the polymer flows less within a forming device when compared to injection molding, the pressure requirements needed to produce an article with a finished shape are less than required with an injection molding machine. This reduced pressure allows pressure sensitive surface materials and cores to be incorporated in the finished composite shape without damage. The processing cycle of the carrier deposited polymer process is similar to an injection molding cycle based on the similar cooling times and distribution of polymer within the forming device. The carrier transfer lower pressure process combines the productivity and processing characteristics of injection molding with the ability to customize the desired finished surface; incorporate cores to improve stiffness, acoustic and insulation properties, and allow selective placement of continuous reinforcement to increase the stiffness and strength of the composite.
The present invention addresses a need in the art by providing a combined polymer matrix where the surface characteristics of the product can be customized, cores can be incorporated and, where needed, reinforcement impregnation to produce a whole new range of useful properties. A carrier, typically in a planar shape, passes below a polymer deposition device where a uniform layer of molten polymer is deposited on the carrier in close proximity to a forming device. The combined materials move into an opening in the forming device where the forming device closes on the materials to form the desired shape.
The carrier moves under a polymer deposition device that contains a predetermined amount of molten polymer based on the size of the deposition chamber. A ram within the chamber pushes the molten polymer out of an opening in the bottom of the chamber where the size and shape of the opening determines the deposited thickness, together with the speed of the ram and carrier. The molten polymer may be polypropylene, high density polyethylene, polyester, thermoplastic olefin or any other desired thermoplastic. The carrier can be low cost non-wovens such as spunbonded polyester and polyolefin or felt; a combination of a film and non-woven or foam; a fluoropolymer film such as Fluronated Ethylene Propylene (FEP) to improve fuel and gas permeation resistance or polyvinyl fluoride for fire retardency and UV resistance; a pre-printed film or a coated film to change the surface characteristics in the finished part or any other desired surface. The combined materials index in a straight line fashion into the forming press where the carrier is separated from a series of side clamps that support the carrier during the deposition and movement phase. Alternately, an undercarriage that holds the carrier in position during polymer deposition and movement into the forming device can support the carrier. A vacuum or clamps incorporated in the undercarriage would hold the carrier and deposited layer or layers of polymer during movement into the forming device, then disengage prior to removal of the undercarriage from the carrier and closing of the forming device. Outboard clamps located on opposite sides of the forming press and outside of the shaping molds would hold and position the combined carrier and deposited polymer as the forming device closed to produce the desired shape. Preferably, the undercarriage would be an insulator and have low surface friction characteristics.
In a second aspect, the carrier moves under the polymer deposition device in a direction away from the forming device as polymer is deposited on the carrier. Once clear of the deposition device, a multi-axis robot positions an insert on top of the deposited polymer layer. The carrier reverses direction, again passing under the polymer deposition device where a second coating or layer of polymer is deposited over the insert. The combined composite moves in a straight-line direction into the forming device to form a desired shape. The insert can be rigid foam, honeycomb, balsa or any other desired construction.
Alternately, two polymer deposition devices can align with each other in a manner where the carrier can pass under both devices in a straight-line direction with the forming device. The carrier first passes under the deposition device furthest from the forming device, then under the second deposition device where a second layer of polymer is deposited. The combined polymers and carrier move into the forming device where the desired shape is formed. Prior to the second deposit a multi-axis robot places an insert such as rigid foam or honeycomb on top of the first deposited layer prior to applying the second coating. The composition of the polymer being deposited from each deposition chamber can be the same or of a different polymer.
Using a secondary chamber that collects molten polymer from the deposition chamber, continuous fibers, discontinuous fibers or a combination of continuous and discontinuous fibers are fed into a chamber where the fibers are encapsulated by molten polymer under pressure and downward applied motion as described in my copending U.S. patent application, Ser. No. 09/388,052, now U.S. Pat. No. 6,264,462. The combined material is deposited in generally a planar shape on the carrier and moves into the forming device to produce the desired shape.
A second surface layer can be applied to the deposited polymer prior to entering the forming device. A multi-axis robot contains a vertical holding fixture with a curved edge on the side closest to the deposited polymer. The surface layer is positioned on the fixture with the edge extending into the curved area. The robot applies downwardly acting pressure on the curved edge where the forward movement of the deposited polymer on the carrier pulls the surface layer from the robot fixture. The curved edge can incorporate a roller feature that assists the movement of the second surface layer. Alternately, drive rollers or other suitable driving devices can assist the forward movement of the second surface layer during lamination to the top of the deposited polymer melt.
A mold consisting of a cavity or concave side and a core or convex side can be attached to a vertical action-forming device such as a clamping press. The desired polymer and carrier composition would be positioned between the cavity and core where the press would close to form the product determined by the shape of the cavity and core. The carrier side can be formed over either the cavity or core. One reason for forming the carrier over the core side would be to produce a chamber with the carrier on the inside area. Two chambers with matching edges would be aligned opposite each other and fused together after softening the surfaces of the carrier edges with a source of heat generation directed at the area to be fused. A set of holding fixtures would move the two mating half""s together under pressure to insure full contact at the bond line. The resulting part would be a hollow device such as a liquid container. Interior and exterior required details would be incorporated in either section of the parts. The use of a fluoropolymer construction as the carrier would provide improved chemical and permeation resistance through the inside walls of the container. A specific example would be a plastic fuel tank with molded-in attachment features and low fuel vapor permeation.
Any of the various carrier and polymer combinations can be incorporated together to form a specific finished article or part. For example, the carrier can provide a decorative surface with the deposited polymer adding structure. The incorporation of a core such as rigid foam between polymer layers can increase the stiffness, insulation properties or other desirable characteristic in the combined composite. Continuous fiber reinforcement in one or both polymer deposits would increase the stiffness and strength of the composite.